Quick answer: Converting an existing space into a food and beverage outlet requires careful planning around exhaust hood sizing, ductwork routing, makeup air, fire suppression, and local code compliance. Retrofitting an exhaust system is often more complex than installing one in new construction because existing structural, electrical, and spatial constraints limit your options. Addressing these ten considerations early prevents costly delays and failed inspections.
Turning a retail unit, warehouse, or old restaurant shell into a functioning commercial kitchen sounds straightforward until you get to the exhaust system. Unlike new-build restaurants, converted spaces come with existing walls, ceiling heights, roof structures, and neighboring tenants that weren’t designed with grease-laden vapor and heat extraction in mind. What looks like a simple hood installation on paper can quickly become the most expensive and time-consuming part of your fit-out.
Getting the exhaust system right isn’t just about passing inspection. It affects your kitchen’s safety, your staff’s comfort, your energy bills, and your ability to operate the type of cooking equipment your menu demands. A commercial kitchen exhaust system that’s undersized, poorly routed, or incompatible with the building’s existing infrastructure can derail your opening timeline by months.
This guide walks through the ten most important exhaust considerations to evaluate before you sign a lease or commit to a layout. Whether you’re converting a strip mall unit into a fast-casual concept or transforming an old office into a full-service restaurant, these factors will shape your budget, your design, and your path to opening day.
1. What type of cooking equipment will determine your hood requirements?
Before anything else, define your menu and equipment list. The type of cooking you’ll be doing determines whether you need a Type I hood (for grease-producing equipment like fryers, griddles, and charbroilers) or a Type II hood (for heat and steam-producing equipment like ovens, steamers, and dishwashers that don’t produce grease).
Type I hoods require far more extensive infrastructure, including grease ductwork, fire suppression systems, and makeup air units. If your concept relies heavily on frying, grilling, or wok cooking, plan for Type I from the outset. Underestimating equipment needs early in the design process is one of the most common reasons conversion projects need costly rework later.
2. Can the existing building structure support your ductwork routing?
New construction allows architects to plan duct chases and roof penetrations from day one. Conversions rarely offer that luxury. You’re working within existing joists, beams, tenant spaces above or beside you, and roof structures that may not have been designed to support additional equipment or duct runs.
Grease duct runs must maintain minimum clearances to combustible materials, typically require enclosure in a fire-rated chase when passing through occupied spaces, and need a relatively direct path to the roof or exterior wall. Before finalizing your kitchen layout, have a mechanical engineer or exhaust specialist assess whether the current structure can accommodate the duct path you need, or whether it will require significant structural modification.
3. Where will the exhaust fan discharge, and who’s affected by it?
Grease exhaust must discharge at a safe distance from windows, air intakes, adjacent buildings, and property lines. In multi-tenant buildings or dense commercial strips, this is one of the biggest constraints in a conversion project. A rooftop unit above a shared building might sit too close to a neighboring tenant’s fresh air intake, or a wall-mounted exhaust might not comply with clearance requirements to a nearby residential property.
Check your local building and mechanical codes for discharge clearance rules before assuming your preferred equipment location will work. If your building has HVAC units, other tenants’ exhaust systems, or operable windows nearby, factor those into your placement decision early, since relocating a rooftop curb after installation is expensive.
4. Does the space have enough makeup air, and where will it come from?
Every cubic foot of air your exhaust hood removes from the kitchen needs to be replaced, or the kitchen will develop negative pressure. Negative pressure causes doors to stick, pilot lights to blow out, and exhaust fans to work harder than they should, driving up energy costs and reducing system performance.
In a conversion, you may need to install a dedicated makeup air unit (MAU) that tempers incoming air to a comfortable temperature before it enters the kitchen. Because retrofitted spaces often lack the roof space, electrical capacity, or ductwork routing for a full MAU, this is a consideration that needs to be resolved at the same time as your exhaust hood selection, not as an afterthought.
5. What fire suppression system does your hood configuration require?
Any Type I hood installation requires an automatic fire suppression system, most commonly a wet chemical system that meets UL 300 standards. In the United States, NFPA 96 sets out the core requirements for ventilation control and fire protection of commercial cooking operations, covering everything from hood construction to duct cleaning access and suppression system design.
When converting a space, check whether it previously operated as a restaurant with an existing suppression system. Older systems that predate UL 300 typically need to be replaced rather than reused, since they were designed for equipment and grease loads that don’t reflect current fire code standards. Even a system that looks intact may not be approved for your new equipment lineup.
6. Is there enough electrical and utility capacity for your exhaust system?
Exhaust fans, makeup air units, and fire suppression system controls all draw power, and larger systems may require three-phase electrical service that an older building doesn’t have. Before finalizing your equipment specifications, confirm the building’s electrical panel has enough capacity, or budget for a service upgrade.
This consideration often gets missed because it sits outside the immediate scope of “exhaust design,” but electrical capacity constraints can just as easily delay your opening as a duct routing problem. Loop your electrician in during the early design phase, not after equipment has been ordered.
7. What do local health and building codes require for hood sizing and airflow?
Exhaust hood sizing isn’t a one-size-fits-all calculation. Local codes typically dictate minimum airflow rates (measured in cubic feet per minute, or CFM) based on the type of cooking equipment beneath the hood and the hood’s style (wall-mounted canopy, island canopy, or backshelf, for example). An undersized hood won’t adequately capture grease and heat, while an oversized one wastes energy and increases makeup air demands.
Because code requirements vary by jurisdiction, work with a mechanical engineer familiar with your local authority having jurisdiction (AHJ) to calculate the correct CFM for your specific equipment lineup. Skipping this step is one of the fastest ways to fail a mechanical inspection.
8. How will you handle grease duct access and cleaning requirements?
Grease ducts require periodic inspection and cleaning to remove accumulated grease, which poses a serious fire risk if left unchecked. Codes typically require cleanout access points at intervals along horizontal duct runs and at changes in direction. In a conversion project, existing ceiling structures, dropped ceilings, or tight duct chases can make it difficult to provide the access panels required for compliant cleaning.
Plan your duct routing with maintenance access in mind from the start. Retrofitting access panels after the ceiling and finishes are complete is disruptive and costly.
9. What’s the realistic timeline for permitting and inspections?
Exhaust system installations in conversion projects typically require multiple permits and inspections, covering mechanical, fire, electrical, and sometimes structural work. Because you’re modifying an existing building rather than building from a blank slate, plan reviewers may require additional documentation showing how new work integrates with existing systems.
Build extra time into your project schedule for potential back-and-forth with your local building and fire departments, particularly if your space has a complicated history of prior uses or code violations. A realistic timeline protects your opening date and your budget.
10. Should you hire a specialist to assess the space before signing a lease?
Many F&B operators sign a lease before fully understanding what an exhaust retrofit will cost. Given how much site-specific factors, like roof access, structural constraints, and neighboring tenants, affect exhaust system feasibility and cost, it’s worth bringing in a mechanical engineer or commercial kitchen exhaust specialist to assess a space before you commit to it.
A pre-lease assessment can reveal deal-breaking issues, such as insufficient roof load capacity or a discharge clearance conflict with a neighboring tenant, before you’re locked into a lease you can’t easily exit. Choose this step if your target space has no prior food service history or has sat vacant for an extended period, since these spaces carry the highest risk of unexpected exhaust infrastructure costs.
Plan your exhaust system before you plan your menu
Converting an existing space into an F&B outlet can save time and money compared to ground-up construction, but only if the exhaust system gets the attention it deserves early in the process. Hood type, ductwork routing, makeup air, fire suppression, and code compliance all interact with each other, and a decision made in one area often constrains your options in another.
Before finalizing a lease or committing to a kitchen layout, bring in a mechanical engineer or exhaust specialist to evaluate the space against your equipment and menu plans. The upfront cost of a professional assessment is small compared to the cost of discovering a fatal flaw after construction has begun.
Frequently Asked Questions
How much does it cost to install a commercial kitchen exhaust system in a converted space?
Costs vary widely depending on hood size, duct routing complexity, and whether the building needs structural or electrical upgrades. Conversion projects tend to cost more than new construction because of unknowns like existing structural constraints and outdated electrical service. Getting quotes from local mechanical contractors after a site assessment is the most reliable way to budget accurately.
How long does it take to install a commercial exhaust system during a conversion?
Timelines depend on permitting complexity, structural modifications, and equipment lead times. Simple installations in buildings with existing infrastructure may take a few weeks, while projects requiring new roof penetrations, electrical upgrades, or extensive duct rerouting can take several months from design to final inspection.
Can I reuse an existing exhaust hood from a previous restaurant tenant?
Sometimes, but only if the hood, ductwork, and fire suppression system meet current code requirements and match your new equipment’s CFM and grease load specifications. Older systems, especially fire suppression systems installed before UL 300 standards, often need replacement rather than reuse.
What’s the difference between a Type I and Type II hood?
A Type I hood is required for equipment that produces grease-laden vapors, such as fryers and grills, and requires grease ductwork and fire suppression. A Type II hood is used for equipment that produces only heat or steam, such as ovens and dishwashers, and has simpler infrastructure requirements.
Do I need a permit to install a commercial kitchen exhaust system?
Yes. Most jurisdictions require mechanical, fire, and sometimes structural permits for commercial kitchen exhaust installations. Requirements vary by location, so confirm the specific process with your local building and fire departments before starting construction.